Many MEPPs show notches or steps on the rising phase and these occur too frequently to arise by chance coincidence. Moreover, after heat challenge, up to 30% of the MEPPs have either a very slow rising phase or exhibit several steps on their rising phase. These observations demonstrate that quanta are not spontaneously released independently. We have shown that there are two general classes of MEPPs, bell-MEPPs and skew-MEPPs. Amplitude histograms of both classes show integral peaks suggesting that the classical quanta result from the synchronous release of subunits. We plan to voltage clamp the junction since currents show a more rapid time course than voltage changes. Measurements of miniature end plate currents should produce clear multi-peaked distributions and lend further support to the subunit hypothesis. Further determinations of acetylcholine in the nerve-muscle preparation will be made after various challenges. The design of these experiments is to determine the immediately available store of transmitter and correlate ultrastructural changes with experimentally altered electrophysiological and biochemical states.